Scientific and Useful

New Zealand Graphic, Volume XXXVII, Issue 22, 1 December 1906, Page 26

Scientific and Useful

!A NEW METHOD OF TUNNELLING. This is an age of tube-rail ways, and tunnels driven Items th the lied of broad rivers have eeased to attract attention as' anything wonderful. Everybody knows that these tunnels bored under rivers are principally dependent upon compressed air to keep the vater from entering during the process of construction. Pumps arc kept constantly at work and air is driven into the bores at a sufficient pressure to counternalance the weight of water outside and prevent it from entering. In the ease of a small tunnel t .is method works fairly satisfactorily; but in the larger tunnels demanded by modern railway construction immense dotieumes have to be faeed. The pressure of water percolating through the river-bed varies, of course, in proportion to the depth below the water-surface, and it follows that the pressure upon the lower portions of the boring is far greater than that upon the upper part. The counterbalancing air-pressure from within must necessarily be sufficiently great to set against the greatest water-pressure—that at the bottom of the tunnel; and this pressure is, therefore, much in excess of what is necessary to keep the water from leaking in through the upper walls. As a consequence of using an air-pressure considerably higher than is necessary to balance the weight of water above,“blowouts'’ frequently occur,and the air rushes with explosive force into the river above. Apart from the grave danger of flooding the works through these occasional blow-outs, there is always the effect of compressed air upon the human workers to lie considered, and many lives are sacrificed in the making of-every subaqueous tunnel because of the distressing effect of the compressed air upon the men who have to work in it. A new method of making large borings without the aid of couipressed air is being thoroughly experimented with by the Pennsylvania Railroad Company. Although at first sight it appears to be a roundabout method of accomplishing the result, it is said that these experiments are justifying the means. Broadly apeaking. the new method consists in boring a small pilot-tunnel a few feet in diameter, using the old compressed air process, and then by means of a refrigerating system freezing the mud mound it so that it can be worked in the solid suite. Within the small pilottunncl a large number of refrigerating tubes is placed, and for a long time freezing mixture is forced through the tubes from a refrigerating station on the almit. This refrigerating is kept in constant operation for several months, and a>l around the pilot-tunnel a core of freezing sand ami mud is gradually increasing in diameter. When this congealed mass has reached the necessary radial distance all round the original boring, the freezing ean be stopjied ami the tunnellers may enter with safety and proceed to enlarge tlip tunnel to the required diameter without any fear of the intrusion of water from without.

BRA KE It OKS E-POWER

Exactly what is meant by "brake-borse-power" is very frequently not in the least understood even by the owners and users of engines of various kinds. The brake-horse-power of an engine is ascertained by attaching to the flywheel or shaft a slipping brake and measuring the pull upon this brake; which pull, calculated in conjunction with the speed fit rotation ami size of the wheel to which the brake is applied, gives the relative power of the engine under test. The method is difficult of application, and contains many possibilities of error. An ingenious aiid remarkably simple device known as the “Sellers’ dynamometer” is described in a recent issue of the “English Mechanic,” and it is said to give Very reliable results. It consists simply of a long lever designed so that its fulcrum rests upon the floor and its short end presses against the underside of the. flywheel of- the engine. Vpon the upper Surface of the lever is a brake-block to

press upon the flywheel. The brakeblock is mounted on four tiny wheels as though it were a small truck in itself, and connected to one end of a spring Iralanec of which the other end is attached to the body of the lever. The method of using this device is as simple as the machine itself. When it is placed in position so that the flywheel is in contact with the brake-block, a suitable weight is placed on the longer end of the lever and shifted from place to place until the most suitable position is found. The rotating flywheel pulls the brakebloek away from the spring balance, which accurately measures the stress. It is simply sufficient to multiply the reading on the balance by the speed of the periphery of the wheel in feet per minute, and divide the result by 33,000 to find the brake-horse-power of the engine. It is believed that a special com]>aet form of this devise is to be placed on the market for the use of owners of motor ears. Doubtless some interesting results may be expected when the figures given by the manufacturers of the ears can be checked by the purchasers.

MOTOR-DRIVEN COM Hi NIED ROAD- ' SWEEPER AND WATERING-CART.

The rapidly increasing use of fast motor cars has made the dust nuisance so intolerable that any appliance designed for its abatement deserves consideration. Messrs. D. Stewart and Compand (Ltd.), of Glasgow, have recently submitted to the Corporation cleansing department a combined ' watering-cart and road-sweeping machine, which, we understand, is doing excellent work. An ordinary Stewart-Thorneyeroft 30 horsepower steam lorry-chassis is fitted at the rear with a rotating brush driven through bevel-gearing from the first mo-tion-shaft of the engine; the intermediate shaft being arranged to swivel, so that the brush may be raised or lowered as desired. A galvanised water-tank capable of holding 1000 gallons is mounted on the rear half of the chassis, and the water is conveyed by means of pipes to two sprinklers placed one on each side of the front of the vehicle. These sprinklers are controlled by valves, and with full water-supply cover a width of roadway 22ft wide. The operations of watering and sweeping ean be carried on simultaneously or separately, and machines of this description will, no doubt, Ire found more useful than the horsedrawn vehicles at present in use.

PROTECTING WOOD AGAINST WHITE. ANTS.

Some time ago reference was made in these columns to a new- process for rendering wood impervious to the attacks of white ants or termites which ordinarily will destroy any woodwork, from domestic timber to railroad sleepers. The new process has been exploited by the I’owefl Wood Process Syndicate, who are now exhibiting a piece of confirmatory evidence of a very conclusive character. Two pieces of ordinary yellow deal yellow deal is considered a toothsome morsel which no healthy-minded white ant would refuse-—-were the subject of a very interesting experiment. One piece was treated in London by this new process, and was afterwards bolted to the other, which was left in its natural condition.' The pieces were then forwarded to the Curator of the Government Botanical Gardens at Singapore, and laid by him—still bolted together—in a place where termites most do congregate. . In a little while the untreated portion of the compound block was almost demolished, whilst its sophisticated fellow remained untouched. They were returned to London before the former had quite disappeared, and they form a splendid testimonial to the efficacy, of the protective process. The solution with which the wood is treated is absolutely odourless and quite unobjectionable from every point of view—except that of the while ant. -